Photo-conductive target comprising both solid and porous layers

ABSTRACT

A compound photo-conductive layer for use in electron gun type image pick-up tubes and the like having a structure consisting of a transparent conductive film, an amorphous porous photoconductive layer deposited in an inert gas atmosphere under low vacuum, and an amorphous solid photo-conductive layer deposited under high vacuum and/or an amorphous intermediate photoconductive layer deposited in a degree of vacuum intermediate between said low vacuum and high vacuum. Either one or both of the solid layer and the intermediate layer has a multi-layer structure consisting of a plurality of sub-layers with a different constituent ratio of photo-conductive material, whereby the photo-sensitivity is increased several times compared to the prior-art compound photo-conductive layer, while also improving the lag characteristic.

United States Patent Watanabe et al.

1111 3,890,524 14 1 June 17, 1975 1 1 PHOTO-CONDUCTIVE TARGET COMPRISING BOTH SOLID AND POROUS Prim ry ExaminerR0bert Segal LAYERS Attorney, Agent, or Firm-Craig & Antonelli [75] Inventors: Rokuro Watanabe; Mitsuhiro Yoshikawa, both of Mobara, Japan [57] ABSTRACT I [73] Assignee: Hitachi, Ltd., Japan A compound photo-conductive layer for use in electron gun type image pick-up tubes and the like having [22] Flled n 1972 a structure consisting of a transparent conductive film, [21] Appl. No.: 266,708 an amorphous porous photo-conductive layer deposited in an inert gas atmosphere under low vacuum,

Cl 313 386. 313 94 and an amorphous solid photo-conductive layer de- [52] 4 31/38 posited under high vacuum and/or an amorphous in- [511 i J A 4 termediate photo-conductive layer deposited in a de- [58] held of l gree of vacuum intermediate between said low vacuum and high vacuum. Either one or both of the solid [56] References Cited layer and the intermediate layer has a multi-layer UNITED STATES PATENTS structure consisting of a plurality of sub-layers with a 2,910,602 10/1959 Lubszynski et a1. 313/65 A different constituent ratio of photo-conductive mate- 2,967.254 1/1961 Forgue a 5 A rial, whereby the photo-sensitivity is increased several Kramer times compared to the prio uart compound photo- 2 2 conductive layer, while also improving the lag characv 0e ze e a.., teristic FOREIGN PATENTS OR APPLICATIONS 1,098,076 1/1968 United Kingdom 313/65 A 15 Clams 7 Drawmg F'gures a O 3- RI 000 $2" s i 0 t a r F; .u 00 Z. 00 0 09 1 000 t 0 ,0; o0 V 3 1 0 s 0 0 q PATENTEDJUN 17 M5 3890. 524

SHEET 1 PATENTEIJJIJN 17 I975 sum 2 a 1d=002 A a gm l kg A g Q 0 LB ILLUMINATION 0N TUBE FACE F007 CANDLES FIG. 7

DARK CU/B'FE/VT (id) l PHOTO-CONDUCTIVE TARGET COMPRISING BOTH SOLID AND POROUS LAYERS This inventionrelates to compound photoconductive layers usedin electrongun type image pick-up tubes such as a vidicon and to the methodof manufacturing the same. 7 j

The compound photo-conductive. layer usually consists'of a transparent conductive layer formed on a transparent substrate such as a glass plate and a photo-. conductive layer formed on the transparent conductive layer.

In such a compound photo-conductive structure, the photo-conductive layer is usually formed by depositing a photo-conductive material such as a group V VI compound, for example, antimony tri-sulfide with an excess content of antimony (usually containing 74, 76 and 78 weight percent of antimony) or arsenic triselenide. The photo-conductive layers formed of these photo-conductive compounds are superior to other types of photo-conductive layers such as those consisting of lead oxide or selenium and selenium compounds, since their dark current and photo-current characteristies with respect to the target voltage are free from saturation, so they are very useful.

Heretofore, there have been compound photoconductive layers of the afore-mentioned compound photo-conductive materials having well-known structures, as referred to in Australian Patent Specification No. 209287. For example, Japanese Patent Publication No. 271/1962 discloses a structure consisting of an amorphous thin solid layer deposited on the transparent conductive film under vacuum of about 10 Torr, a porous layer deposited on the solid layer in an inert gas atmosphere under low vacuum, and a second solid layer the same as the first one deposited on the porous layer. Japanese Patent Publication No. 12008/1965 discloses another structure, which includes an amorphous intermediate layer deposition formed under an intermediate vacuum degree, for instance l0 Torr, and intervening either between an amorphous porous layer and an amorphous solid layer .or between the porous layer and the transparent conductive material.

Both these structures, however, have shortcomings in the aspects of photo-sensitivity and lag characteristic. in particular, they cannot sufficiently meet requirements for use in color image pick-up tubes. Besides, the photo=sensitivity and lag characteristics usually run counter to each other, that is, efforts to increase the photo-sensitivity would usually result in increased lag time.

, The primary object of the invention is to provide a compound photo-sensitive layer and the method of manufacturing the same, which provide for obtaining several times as high photo-sensitivity as that of the prior-art compound photo-conductive layer as well as obtaining improved lag characteristic.

According to the invention, there is provided a compound photo-conductive layer for use in electron gun type pick-up tubes comprising a transparent conductive film, a first thin amorphous solid layer provided on said conductive layer, a second thin amorphous layer, and a porous layer intervening between said first and second thin amorphous solid layers, allsaid layers con taining a photo-conductive material, at least one of said solid layers having a--multi-layer structure consisting of a plurality of sub-layers with a different ratio of constituents of photo-conductive material.

Also, according to the invention there is provided a method of manufacturing a componud photoconductive layer for use in electron gun type pick-up tubes comprising the steps of depositing an evaporated photo-conductive material under high vacuum on a transparent conductive film to form a thin amorphous solid layer, depositing said photo-conductive material in an inert gas atmosphere under low vaccum on said solid layer to form an amorphous porous layer, and forming a second solid layer similar to said firstmentioned solid layer on said porous layer by using the process for forming said first-mentioned solid layer, at least one of said steps of forming said solid layers including sub-steps of depositing antimony tri-sulfide with an antimony content of 74 to 78 weight percent to form a first solid sub-layer, and then depositing on said first sub-layer antimony tri-sulfide with an antimony content greater than that for said first sub-layer under the same vacuum degree as for said first sub-layer, thereby forming a multi-layer structure consisting of a plurality of solid sub-layers with successively greater antimony contents.

The invention is based on the finding that by forming at least one of the solid layers and/or intermediate layers constituting the compound photo-conductive layer by laminating a plurality of sub-layers with a different ratio of constituents of photo-conductive material, the

photo-sensitivity for the same dark current can be increased several times compared to the prior-art compound photo-conductive layer while providing roughly the same voltage-current characteristics. The reason why this is so is not clear, but it is presumable that if a solid layer or intermediate layer where much light energy is absorbed to produce a great deal of electronhole pairs, consists of=-a plurality of sub-layers with a different ratio of constituents of photo-conductive material, for instance the antimony contents of antimony tri-sulfide as will be described hereinafter, the electric field gradient will be different for the individual sublayers, providing for increased field intensity to increase the charge stored on the photo-conductive layer surface.

Further, according to the invention the photosensitivity and lag characteristic do not run counter to each other, so that itis possible to improve both the characteristics.

Furthermore, by appropriately selecting the disposition of the solid layers and intermediate layers it is possible to reduce image burn, which is a type of lag phenomenon.

The above and other objects, features and advantages of the invention .will become more apparent from the following description when read with reference to the accompanying drawing, in which:

FIG. 1 is a sectional view showing an example of the television pick-up tube using a compound photoconductive layer according to the invention;

FIGS. 2 to 5 are fragmentary sectional views, to an enlarged scale, showing examples of the compound photo-conductive layer according to the invention;

FIG. 6 is a graph showing light transfer characteristics of a compound photo-conductive layer according to the invention and a prior-art compound photoconductive layer; and

FIG. 7 is a graph showing dark current characteristics of a compound photo-conductive layer according to the invention and a prior-art compound photoconductive layer.

Referring now to FIG. 1, which shows an example of the television pick-up tube using a compound photoconductive layer according to the invention, reference numeral 1 designates a glass tube envelope, numeral 2 an electron gun, numeral 3 a glass face plate, numeral 4 a transparent conductive layer, and numeral 5 a com- I pound photo-conductive layer.

FIG. 2 shows the structure of the compound photoconductive layer. It is obtained by depositing on the transparent conductive layer 4 provided on the glass face plate 3, evaporated antimony tri-sulfide containing 74 percent of antimony under a vacuum of Torr to form a first intermediate amorphous sub-layer m about 200 A thick, depositing on the sub-layer m anti-' mony tri-sulfide with a greater content of antimony than for the sub-layer m namely containing 76 percent of antimony, under the same vacuum degree to form a second intermediate, similarly amorphous sublayer m about 200 A thick, and further depositing thereon antimony tri-sulfide with a still greater antimony content compared to the sub-layers m and m namely containing 78 percent of antimony, under the same vacuum degree to form a third intermediate sublayer m about 200 A thick, thereby forming an intermediate layer m of a multi-layer structure consisting of the sub-layers m m and m over-lapping one upon another, thereafter depositing on the intermediate layer m antimony tri-sulfide with an antimony content of 74 percent in the atmosphere of such inert gas as argon and helium under a low vacuum degree of 10 Torr to form an amorphous porous layer P about 2 microns thick, and finally depositing on the porous layer P antimony tri-sulfide with an antimony content of 76 percent under a high vacuum degree of 10* Torr to form an amorphous solid layer 8, as thick as about 1,000 A. 7

FIG. 3 shows another example of the compound photo-conductive layer according to the invention. It is obtained by depositing on the transparent conductive layer antimony tri-sulfide with an antimony content of 76 percent under an intermediate vacuum degree of 10 Torr to form an intermediate amorphous layer m of a single layer structure and having a thickness of about 800 A, depositing on the intermediate layer m antimony tri-sulfide with an antimony content of 74 percent in an inert gas atmosphere such as argon or helium gas atmosphere under low vacuum to form an amorphous porous layer P about 2 microns thick, and subsequently depositing on the porous layer P antimony tri-sulfide with an antimony content of 74 percent under a high vacuum degree of 10 Torr to form a first amorphous solid sub-layer S about 1,000 A thick and depositing thereon antimony tri-sulfide with an antimony content, greater than that for the sub-layer S namely 76 percent, under the same vacuum degree to form a second amorphous solid sub-layer S about 2,000 A thick, thereby forming a solid layer S of a multi-layer structure consisting of the sub-layers S and S overlapping one upon another.

FIG. 4 shows a further example of the compound photo-conductive layer according to the invention. This example comprises a solid layer 8,, formed on. the transparent conductive film 4 and having a multi-layer 4 structure 'consistinglof first andsecond solid sub-layers S and S a porous layer P having a singlelayer structure, and asecond solid layer 8., having a multi-layer structure consistingof first 'and secondsolid sub-layers S and S The contentof antimony in the solid sublayers ,8 an;d=S S ismade such that it is smaller I for sub-layers nearer the transparent conductive film 4.

It ranges between 74 and 78 percent for the individual layers and sub-layers. It has been experimentally made apparent that there are no particular limitations imposed upon the relation of the antimony content between the sub-Iayers S and S or between the sublayers S. and S FIG. 5 shows a still further example of the compound photo-conductive layer according to the invention. This example comprises a solid layer S formed on the transparent conductive film 4 and consisting of first and second solid sub-layers S and S a porous layer P having a single layer structure, an intermediate layer m consisting of first and second intermediate sublayers m and "132, and a second solid layer S consisting of first and second solid sub-layers S and S Similar to the preceding examples of FIGS. 2 to 5, the content of the photo-conductive material in the individual layers having multi-layer structure is smaller for sublayers nearer to the transparent conductive film 4, that is, it is smaller for the first sub-layer S compared to the second sub-layer S This also applies to the sublayers m and m and S and S the content is smaller for the first sub-layer in either multi-layer structure layer. The antimony content for the individual layers and sub-layers ranges between 74 and 78 weight percent, while in case of using arsenic tri-selenide the arsenic content for these layers ranges between 41 and 47 weight percent.

FIG. 6 shows light transfer characteristics of the compound photo-conductive layer according to the invention and the prior-art compound photo-conductive layer. Curve A represents the characteristic of the layer having the structure shown in FIG. 2 according to the invention, and curve B represents that of a prior-art layer of the same structure as the FIG. 2 one except that the intermediate layer is of a single layer structure of antimony tri-sulfide with an antimony content of 76 weight percent.

FIG. 7 shows dark current characteristics of compound photo-conductive layers according to the invention and of the prior art. In the Figure, the abscissa represents voltage impressed on the transparent conductive film, and the ordinate the dark current value. The solid curve is obtained for asolid layer or intermediate layer of a multi-layer structure according to the invention, and the dashed curve is obtained for a prior-art solid layer of intermediate layer. It will be seen that according to the invention the dark current is extremely reduced, and also non-ohmic characteristics can be obtained.

Though the foregoing. embodiments have been described by employing antimony tri-sulfide as the photoconductive material only by way of example, it is to be noted that substantially the same results can be obtained by using arsenic tri-selenide in place of antimony tri-sulfide. I

What we claim is; I V

l. A compound photo-conductive target for use, in electron gun type pick-up tubes comprising a transparent conductive film a first thin amorphous solid layer provided on said conductive film, a second thin amorphous solid layer, and a porous layer intervening between said first and second thin amorphous solid layers, all of said layers being formed of a photo-conductive material selected from the group essentially consisting of antimony trisulfide and arsenic triselenide, at least one of said solid layers having a multi-layer structure consisting of a plurality of sub-layers, the antimony or arsenic content of said photo-conductive material in said sub-layers being greater for sub-layers successively remote from said transparent conductive film.

2. The compound photo conductive target according to claim 1, wherein said photo-conductive material is antimony tri-sulfide (Sb S and the antimony content thereof in the multi-layer structure is greater for sublayers successively remote from said transparent conductive film.

3. The compound photo-conductive target according to claim 2, wherein the content of antimony in the individual layers and sub-layers is in a range between 70 and 80 weight percent.

4. The compound photo-conductive target according to claim 1, wherein said photo-conductive material is arsenic triselenide (As Se and the arsenic content thereof in the multi-layer structure is greater for sublayers successively remote from said transparent conductive film.

5. The compound photo-conductive target according to claim 4, the content of arsenic in the individual layers and sub-layers is in a range between 35 and 50 weight percent.

6. The compound photo-conductive target according to claim 1, further comprising an intermediate amorphous photo-conductive layer intervening between one of said solid layers and said porous layer.

7. The compound photo-conductive target according to claim 6, wherein said intermediate layer has a multilayer structure consisting of a plurality of sub-layers formed of a photoconductive material selected from the group essentially consisting of antimony trisulfide and arsenic triselenide the antimony or arsenic content in said photo-conductive compound being greater for the sub-layers successively remote from said transparent conductive film.

8. The compound photo conductive target according to claim 7, wherein said photo-conductive material is antimony tri-sulfide.

9. The compound photo-conductive target according to claim 8, the content of antimony in the individual layers and sub-layers is in a range between 70 and 80 percent.

10. The compound photo-conductive target according to claim 7, wherein said photo-conductive material is arsenic tri-selenide.

11. The compound photo-conductive target according to claim 10, wherein the content of arsenic in the individual layers and sub-layers is in a range between 35 and 50 weight percent.

12. A compound photo-conductive target having a structure consisting of a transparent conductive film, an amorphous porous layer deposited in an inert gas atmosphere under low vacuum, and an amorphous solid layer deposited under high vacuum and an amorphous intermediate layer deposited in a degree of vacuum intermediate said low vacuum and said high vacuum, all said layers containing a photo-conductive material selected from the group essentially consisting of antimony trisulfide and arsenic triselenide, at least one of said solid layer and said intermediate layer having a multi-layer structure consisting of a plurality of sublayers, the antimony or arsenic content of said photoconductive material in said sub-layers being greater for sub-layers successively remote from said transparent conductive film.

13. A compound photo-conductive target having a structure consisting of a transparent conductive film, an amorphous porous layer deposited in an inert gas atmosphere under low vacuum, and an amorphous intermediate layer deposited in a degree of vacuum intermediate said low vacuum and said high vacuum, all said layers containing a photo-conductive material of the V-VI group of compounds, at least one of said solid layer and said intermediate layer having a multi-layer structure consisting of a plurality of sub-layers, the V- group element content of said photo-conductive material being greater for sub-layers successively remote from said transparent conductive film.

14. A compound photo-conductive target for use in eletron gun type pick-up tubes comprising a transparent conductive film, a first thin amorphous solid layer provided on said conductive film, a second thin amorphous solid layer, and a porous layer intervening between said first and second thin amorphous solid layers, all of said layers consisting essentially of a photoconductive material of the V-Vl group of compounds, at least one of said solid layers having a multi-layer structure consisting of a plurality of sub-layers, the V- group element content of said photo-conductive material being greater for sub-layers successively remote from said transparent conductive film.

15. A compound photo-conductive target having a structure consisting of a transparent conductive film, an amorphous porous layer deposited in an inert gas atmosphere under low vacuum, and an amorphous solid layer deposited under highvacuum and an amorphous intermediate layer deposited in a degree of vacuum intermediate said low vacuum and said high vacuum, all said layers containing a photo-conductive material of the V-VI group of compounds, at least one of said solid layer and said intermediate layer having a multi-layer structure consisting of a plurality of sub-layers, the V- group element content of said photo-conductive material being greater for sub-layers successively remote from said transparent conductive film. 

1. A compound photo-conductive target for use in electron gun type pick-up tubes comprising a transparent conductive film, a first thin amorphous solid layer provided on said conductive film, a second thin amorphous solid layer, and a porous layer intervening between said first and second thin amorphous solid layers, all of said layers being formed of a photo-conductive material selected from the group essentially consisting of antimony trisulfide and arsenic triselenide, at least one of said solid layErs having a multi-layer structure consisting of a plurality of sub-layers, the antimony or arsenic content of said photo-conductive material in said sub-layers being greater for sub-layers successively remote from said transparent conductive film.
 2. The compound photo-conductive target according to claim 1, wherein said photo-conductive material is antimony tri-sulfide (Sb2S3), and the antimony content thereof in the multi-layer structure is greater for sub-layers successively remote from said transparent conductive film.
 3. The compound photo-conductive target according to claim 2, wherein the content of antimony in the individual layers and sub-layers is in a range between 70 and 80 weight percent.
 4. The compound photo-conductive target according to claim 1, wherein said photo-conductive material is arsenic tri-selenide (As2Se3), and the arsenic content thereof in the multi-layer structure is greater for sub-layers successively remote from said transparent conductive film.
 5. The compound photo-conductive target according to claim 4, the content of arsenic in the individual layers and sub-layers is in a range between 35 and 50 weight percent.
 6. The compound photo-conductive target according to claim 1, further comprising an intermediate amorphous photo-conductive layer intervening between one of said solid layers and said porous layer.
 7. The compound photo-conductive target according to claim 6, wherein said intermediate layer has a multi-layer structure consisting of a plurality of sub-layers formed of a photoconductive material selected from the group essentially consisting of antimony trisulfide and arsenic triselenide the antimony or arsenic content in said photo-conductive compound being greater for the sub-layers successively remote from said transparent conductive film.
 8. The compound photo-conductive target according to claim 7, wherein said photo-conductive material is antimony tri-sulfide.
 9. The compound photo-conductive target according to claim 8, the content of antimony in the individual layers and sub-layers is in a range between 70 and 80 percent.
 10. The compound photo-conductive target according to claim 7, wherein said photo-conductive material is arsenic tri-selenide.
 11. The compound photo-conductive target according to claim 10, wherein the content of arsenic in the individual layers and sub-layers is in a range between 35 and 50 weight percent.
 12. A compound photo-conductive target having a structure consisting of a transparent conductive film, an amorphous porous layer deposited in an inert gas atmosphere under low vacuum, and an amorphous solid layer deposited under high vacuum and an amorphous intermediate layer deposited in a degree of vacuum intermediate said low vacuum and said high vacuum, all said layers containing a photo-conductive material selected from the group essentially consisting of antimony trisulfide and arsenic triselenide, at least one of said solid layer and said intermediate layer having a multi-layer structure consisting of a plurality of sub-layers, the antimony or arsenic content of said photo-conductive material in said sub-layers being greater for sub-layers successively remote from said transparent conductive film.
 13. A compound photo-conductive target having a structure consisting of a transparent conductive film, an amorphous porous layer deposited in an inert gas atmosphere under low vacuum, and an amorphous intermediate layer deposited in a degree of vacuum intermediate said low vacuum and said high vacuum, all said layers containing a photo-conductive material of the V-VI group of compounds, at least one of said solid layer and said intermediate layer having a multi-layer structure consisting of a plurality of sub-layers, the V-group element content of said photo-conductive material being greater for sub-layers successively remote from said transparEnt conductive film.
 14. A COMPOUND PHOTO-CONDUCTIVE TARGET FOR USE IN ELECTRON GUN TYPE PICK-UP TUBES COMPRISING A TRANSPARENT CONDUCTIVE FILM, A FIRST THIN AMORPHOUS SOLID LAYER PROVIDED ON SAID CONDUCTIVE FILM, A SECOND THIN AMORPHOUS SOLID LAYER, AND A POROUS LAYER INTERVENTING BETWEEN SAID FIRST AND SECOND THIN AMORPHOUS SOLID LAYERS, ALL OF SAID LAYERS CONSISTING ESSENTIALLY OF A PHOTO-CONDUCTIVE MATERIAL OF THE V-VI GROUP OF COMPOUNDS, AT LEAST ONE OF SAID SOLID LAYERS HAVING A MULTI-LAYER STRUCTURE CONSISTING OF PLURALITY OF SUB-LAYERS, THE V-GROUP ELEMENT CONTENT OF SAID PHOTO-CONDUCTIVE MATERIAL BEING GREATER FOR SUB-LAYERS SUCCESSIVELY REMOTE FROM SAID TRANSPAR ENT CONDUCTIVE FILM.
 15. A compound photo-conductive target having a structure consisting of a transparent conductive film, an amorphous porous layer deposited in an inert gas atmosphere under low vacuum, and an amorphous solid layer deposited under high vacuum and an amorphous intermediate layer deposited in a degree of vacuum intermediate said low vacuum and said high vacuum, all said layers containing a photo-conductive material of the V-VI group of compounds, at least one of said solid layer and said intermediate layer having a multi-layer structure consisting of a plurality of sub-layers, the V-group element content of said photo-conductive material being greater for sub-layers successively remote from said transparent conductive film. 